1. Field of the Invention
The present invention relates to electrophotographic photosensitive members and more particularly to electrophotographic photosensitive members containing hydrazone group compounds.
2. Description of the Prior Art
Inorganic photoconductive substances such as selenium, cadmium sulfide, and zinc oxide have so far been used over a wide range in photosensitive layers of electrophotographic photosensitive members. The photosensitive members employing such inorganic photoconductors involve various disadvantages along with several advantages. Examples of the disadvantages are as follows: In the case of selenium, the production cost of the photosensitive member is high because of its low productivity, severe conditions of production, and loss of the raw material, which are attributable to the vacuum deposition process, and in addition the deposited film of selenium itself has extremely poor resistance to heat and mechanical shocks and is very liable to crystallize under certain environmental conditions. In the case of a photosensitive member made of cadmium sulfide, the photosensitive member stored under high humidity cannot exhibit stable sensitivity or durability upon using. In the case of a photosensitive member made of zinc oxide, the photosensitive member is subject to charge deterioration and light fading due to corona charging, since the sensitization is effected by use of a dye of poor fastness, typified by Rose Bengal. This type of photosensitive member has also disadvantages in smoothness, hardness, and wear resistance of the photosensitive layer surface thereof because it is a dispersion system of zinc oxide particles in a resin.
In contrast to inorganic photoconductive substances, organic ones have the advantage of giving a highly flexible photosensitive layer and photosensitive members of stable electrophotographic characteristics with ease and low costs, so that in recent years many proposals have been made.
The following types of photosensitive members are known as those employing organic photoconductive substances:
(1) A charge-transfer complex is formed by combining an electron donor with an electron acceptor (e.g. U.S. Pat. No. 3,484,237).
(2) An organic photoconductor is sensitized by addition of a dye (e.g. Japanese Patent Publication No. 25,658/1973).
(3) A pigment is dispersed in a positive hole matrix or an electronically active matrix (e.g. U.S. Pat. Nos. 3,894,868 and 3,870,516).
(4) An electrophotographic photosensitive member comprises a charge generation layer and a charge transport layer (e.g. U.S. Pat. No. 3,837,851).
(5) An electrophotographic photosensitive member comprises a co-crystalline complex containing a dye and a resin (e.g. U.S. Pat. No. 3,684,502).
(6) An organic pigment or an inorganic charge generation material is added to a charge-transfer complex (e.g. U.S. Pat. No.3,775,105).
(7) Other types.
Present aspects of these types of photosensitive members are that further improvements in sensitivity, durability, environmental stability, etc. are desired though actually useful ones are found among them.
These organic photoconductive substances for such photosensitive members include high-molecular compounds typified by poly(N-vinylcarbazole) and low-molecular compounds such as pyrazoline derivatives disclosed in U.S. Pat. No. 3,837,851.
High-molecular photoconductive substances generally give brittle coatings and are deficient in film forming property and in flexibility. Addition of a plasticizer to remove these drawbacks is accompanied by alternative drawbacks such as reduction of sensitivity. On the other hand, low-molecular ones can be freed from such drawbacks as high-molecular ones have, by choosing a proper binder, but cannot be said to be satisfactory in sensitivity, durability, and environmental stability.
Sensitivity of conventional photosensitive members, which is represented in exposure quantity for halving original potential, E 1/2 is about 15 lux.multidot.sec for unsensitized Se type and in the order of 4-8 lux.multidot.sec for sensitized Se type. Sensitivity of CdS type is similar to that of sensitized Se type, and that of ZnO type about 7-12 lux.multidot.sec.
As a desirable sensitivity of practical photosensitive member, E 1/2 value is to be 20 lux.multidot.sec or lower in the case of a usual PPC copying machine, more preferably 15 lux.multidot.sec or lower in the case of a high-speed PPC copying machine, but a photosensitive member of sensitivity lower than that mentioned above may be used.